1. FIELD OF THE INVENTION
The present invention relates to a cassette for accommodating a magnetic recording medium. More particularly, it relates to a cassette for stably positioning a magnetic recording medium, such as a magnetic disc sheet in the form of a floppy disc, which is accommodated in the cassette.
2. DESCRIPTION OF THE PRIOR ART
One prior art example of a cassette or jacket for accommodating a magnetic recording medium is shown in FIG. 1. In FIG. 1, the cassette which is denoted by reference numeral 1, is in the form of a flat case or member consisting of a pair of cassette halves 1a, defining a cavity therebetween. The halves 1a each have a substantially rectangular shape and are made of a synthetic resin. The cassette 1 accommodates a magnetic disc 2 having a central circular spindle drive hole 2a, the disc rotating within the cavity about an axis normal to the surfaces of the cassette halves 1a. A window or opening 3 is formed in the central portion of the cassette 1, the opening 3 being concentric with the hole 2a and having a larger diameter than the hole 2a.
The cassette 1 has a head window or opening 4 which exposes the magnetic disc 2 over a given length in the radial direction of the disc. The head window 4 is positioned so that a magnetic head located within a magnetic recording/reproducing apparatus projects into the window 4 when the cassette 1 is loaded into the magnetic recording/reproducing apparatus. The magnetic head cooperates with the magnetic disc 2 to selectively record information on the disc and to reproduce information previously impressed on the disc. A center cone, which functions as a disc clamp, and a spindle, which acts as a driving mechanism of the magnetic recording/reproducing apparatus, engage each other through the hole 2a and opening 3.
A liner (not illustrated) is attached to the inner surface of the cassette 1 in order to prevent the magnetic disc 2 from contacting directly the cassette 1 and causing damage to the magnetic disc 2.
FIG. 2 illustrates a cassette for accommodating a magnetic recording medium which is an improvement over that illustrated in FIG. 1. In FIG. 2, a movable head shutter 5 is provided inside the cassette 1 behind the head window 4. The shutter 5 comprises a plate, having its surfaces parallel to the disc 2, which covers the entire area of head window 4.
A pin 6 projects from a surface of the shutter 5 and extends through a guide slot 7 in the cassette half 1a, the slot 7 being located in the vicinity of the head window 4 between the window 4 and the opening 3 of the cassette half 1a. The pin 6 is slidable along the guide slot 7 so that the window 4 can be opened or closed by the head shutter 5, shutter 5 being moved by sliding the pin 6 along the guide slot 7 with the use of a fingertip or suitable tool.
Therefore, if the head shutter 5 is moved by the pin 6 to a position where the head window 4 is closed when the cassette 1 is not in use, the invasion of dust into the inside of the cassette 1 through the head window 4, or the direct contact of a fingertip of an operator with the magnetic disc 2, are prevented. Accordingly, the magnetic disc 2 is kept clean and without scratches or other damage to its surface.
The cassette halves 1a which comprise the cassette 1 are usually made of a relatively rigid material such as a rigid synthetic resin. The magnetic disc 2, which is accommodated in the cassette 1 and rotates in a given direction, consists of a base comprising a very thin flexible material that is easily subjected to elastic deformation. The base material can be a synthetic resin, and a coating of magnetic material is applied to the base.
As a result, when the center cone is inserted into the opening 2a and the driving spindle for transmitting a rotating force to the disc 2 is engaged with the center cone so as to hold the disc 2 between the cone and the driving spindle during a recording/reproducing operation, the magnetic disc 2 is distorted when loaded or undulated while rotating. It may also happen that the magnetic disc 2 is deformed by the magnetic head pressing on the disc.
Such deformation causes a spacing loss between the magnetic head and the magnetic disc 2, and a spacing or deviation of the tracks on the magnetic disc 2 during the recording/reproducing operation. Consequently, it is very difficult to carry out recording with a high recording density, and the reliability of the magnetic recording/reproducing apparatus is deteriorated.